The present invention relates to a non-impact electric image transfer recording method, and more particularly to a non-impact electric image transfer recording method by making use of a shrinkage and expansion phenomenon of a polymer gel when voltage is applied thereto, which image transfer recording method is capable of yielding clear images on a transfer sheet with clear background even if image transfer is made in repetition to a number of transfer sheets.
In accordance with the remarkable development of computers and facsimile apparatus, printers which serve as the terminal apparatus therefor are unquestionably important apparatus in such fields. Such printers can be roughly classified into two categories, an impact-type printer (i.e., a mechanical printer) and a non-impact-type printer. As to the recording systems for use with the non-impact-type printer, the following five systems are known: (1) electro-photographic system, (2) thermosensitive coloring system, (3) electric discharge system, (4) thermosensitive image transfer system, and (5) non-impact electric or electro-thermic image transfer system. The former impact-type printer has the inevitable shortcoming that it generates noise during operation because of its mechanical structure.
In contrast to this, the latter non-impact type printer has the advantage that it does not generate noise during operation, but has several problems in each recording system as well. Among these recording systems, the above-mentioned (5) electric image transfer system (electric image transfer recording system) has the advantages that images can be obtained with high resolution directly on a sheet of plain paper with high recording speed, and the apparatus for this system can be made compact in size.
Further, a method of electrothermally heating an ink-continuing porous thermal head imagewise, thereby transferring the ink imagewise to a transfer sheet has been reported, for instance, in Summary of Lectures of National Convention No. 1295, the Institute of Electronics and Communication Engineers, 1985. This method has many excellent advantages, but also has the shortcoming that clear images cannot be obtained when transferred to a number of transfer sheets because of the occurrence of the fogging in the background, and image tailing.
Furthermore, in Japanese Laid-Open patent application 62-124980, there is proposed another method of electrothermally transferring images to a transfer sheet comprising the two steps of (i) softening a thermally transferable ink contained in an ink roller which comprises a porous material impregnated with the ink by application of heat or a voltage to the ink roller and (ii) transferring the softened ink to a sheet of paper with application of pressure.
This method, however, has the shortcoming that it is difficult in principle to keep the ink softened during the two steps, so that printed images are apt to become uneven in image density and some portions of the images are unprinted.
Furthermore, in Japanese Laid-Open patent application 62-5889, there is proposed a thermal image transfer recording method by making use of the shrinkage of a polymer gel, in which an aqueous-ink-containing polymer gel is shrunk by heating the same with a thermal head, so that the aqueous ink is caused to ooze imagewise onto a printing sheet. In this recording method, the polymer gel can be used in repetition by replenishing the aqueous ink to the gel and reswelling the same from time to time. This method, however, has the shortcoming that the thermal response of the polymer gel is considerably slow, for example, as long as more than 5 ms for a 1 .mu.m thick polymer gel layer.
Moreover, in Japanese Laid-Open patent application 60-60690, there is shown a recording method in which an ink-containing-polymer gel is shrunk under the conditions where the phase transition of the polymer gel takes place, with the voltage application thereto as being one of such conditions. In this patent application, it is merely described that the ink can be replenished by dipping the polymer gel into the ink. However, this method has in fact the shortcoming that it takes several hours for the polymer gel to get back to its original state just by dipping the polymer gel into the ink.